The present invention relates to an apparatus for performing color image printing, and more particularly relates to a small-size color image printing apparatus utilizing an electro-photographic process.
In the past, there has been an electro-photographic printing apparatus utilizing electro-photography for printing a color image using image information from a computer or the like. The use of electro-photography has a disadvantage in that it calls for a complex structure, which is difficult to handle and is large in size, because of the large number of printing processes to be carried out therein. Particularly, if the apparatus is arranged to provide developing units for four colors arranged around a photosensitive drum, the apparatus becomes complex in that each of the developing units is required to change its structure and at the same time the diameter of the photosensitive drum becomes large. Therefore, in a conventional apparatus of this type, a photosensitive body having a comparatively small diameter is employed, and at the same time a switching method using a mechanism for sliding or rotating the four developing units into an operative position is also employed. This technology is described in, for example, Japanese Patent Application Laid-Open No. 2-189562 (1990) and Japanese Patent Publication No. 2-13304 (1990). However, the apparatus having this construction is complex and not easy to handle because of the mechanism required for driving the developing units.
On the other hand, a method is proposed in Japanese Patent Application Laid-Open No. 2-213884 (1990), where a photosensitive body is formed as a belt, and three or four developing unit are arranged to make use of the flat surface portion of the photosensitive belt.
However, it has been difficult for the conventional electro-photographic apparatuses to satisfy quality of image, speed of printing, easiness of maintenance and size of apparatus requirements at one time. There occurs any one or more of a degradation in the quality of the image, a lowering in speed of the printing and an increase in the size of the apparatus. Therefore, although various methods have been proposed, it has not been possible to provide a high-quality-image and small-size color electro-photographic apparatus having a size capable of use as a desk-top apparatus.
An object of the present invention is to provide a small-size color electro-photographic apparatus having a size which makes it capable of easily being used as a desk-top apparatus and which satisfies quality of image, speed of printing, and easiness of maintenance requirements at one time by systematically studying printing processes of such components as a photosensitive belt, an intermediate transfer drum charging unit, an exposing unit, a developing unit, a transfer unit, a fixing unit and so on, a paper transporting path, and construction and arrangement including unitizing each of the components.
In order to attain the above object, a drum is employed as the intermediate transfer component and a photosensitive belt having a length equal to the outer peripheral length of the intermediate transfer drum is arranged with a vertical orientation. Developing units of the same shape are arranged in one side of the photosensitive belt, and a charging unit and a cleaner are arranged in the other side thereof. The intermediate transfer drum is placed under or diagonally under the photosensitive belt. A transfer mechanism for transferring an image on the intermediate transfer drum to a sheet of paper is placed under or diagonally under the intermediate transfer drum.
In the above construction, it is possible to get the rotating cycle of the photosensitive belt to agree with that of the intermediate transfer drum by employing a photosensitive belt having a length equal to the peripheral length of the intermediate transfer drum. Therefore, it is easy to obtain sufficient accuracy of color superposition in superposing an image of each color. In the above construction, it is also possible to reduce the entire size of the apparatus by employing a photosensitive belt having a length equal to the peripheral length of the intermediate transfer drum. Further, it is comparatively easy to construct a thin developing apparatus because the photosensitive body of belt-shape is arranged vertically and the developing units are arranged in one side of the photosensitive body. Furthermore, it is possible to place the means for transferring an image to paper in a position under the intermediate transfer drum where is effective to peel off the paper because the intermediate transfer drum is placed under the photosensitive belt.